Mitochondrion-dividing ring in an alga Nannochloropsis oculata (Eustigmatophyceae, Heterokonta)

Abstract

The mitochondrion-dividing ring (MD ring) is an electron-dense annular structure at the isthmus of constricting mitochondria, which was first found in a primitive red alga Cyanidioschyzon merolae (Kuroiwa et al. 1993, 1995). However, there has been no evidence for its existence in other organisms. In the present study, mitochondrial division of a unicellular eustigmatophyte alga Nannochloropsis oculata was examined by transmission electron microscopy. Three-dimensional reconstruction of serial thin sections revealed the MD ring girdling the isthmus of the constricting mitochondria. This suggests that the MD ring is conserved in eustigmatophytes distant from rhodophytes in phylogeny.